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<DIV CLASS="navbar"><A HREF="http://vt100.net/"><IMG CLASS="button" SRC="vt100.net-logo.png" ALT="VT100.net" HEIGHT="16" WIDTH="102"></A> LA100-Series Programmer Reference Manual<TABLE WIDTH="100%">
<COL SPAN="3" WIDTH="33%">
<TBODY>
<TR>
<TD ALIGN="LEFT"><A HREF="intro.html">Introduction</A></TD>
<TD ALIGN="CENTER"><A HREF="contents.html">Contents</A></TD>
<TD ALIGN="RIGHT"><A HREF="chapter2.html">Chapter 2</A></TD>
</TR>
</TBODY>
</TABLE>
<HR></DIV>
<H1 ID="S1"><SPAN CLASS="chapnum">1</SPAN> Communication</H1>
<H2 ID="S1.1">General</H2>
<P>This chapter describes LA100 communication interfaces and the
terminal communication features. The communication features are
used to configure the terminals to operate with specific
computers. This chapter also discusses the methods of controlling
data received by the terminal to avoid input buffer overflows.</P>
<H2 ID="S1.2">Serial Character Format</H2>
<P>The LA100 communicates using serial characters (<A HREF="#F1-1">Figure 1-1</A>). The
serial character format for the terminal must match the character
format used by the computer. Serial characters are transmitted
using a start bit, 7 or 8 data bits, a selectable parity bit and 2
stop bits.</P>
<P CLASS="note">NOTE: If you are using the LA12X-BB Parallel Interface option,
refer to the option installation guide for character format
information.</P>
<P>The data bits represent a 7 bit character, least significant bit
leading. If 8 bit characters are selected, the last data bit is
forced to the space (0) condition and the eighth data bit is
ignored when receiving characters. The parity bit is operator
selectable.</P>
<TABLE ID="F1-1">
<CAPTION>Figure 1-1 Serial Character Format</CAPTION>
<TBODY>
<TR>
<TD><IMG SRC="ma-7815a.png" ALT=""></TD>
</TR>
</TBODY>
</TABLE>
<H2 ID="S1.3">Break Signal</H2>
<P>A break signal is a transmitted space condition for 0.275 seconds
&plusmn;10 percent. The computer response to the break signal depends on
the computer and the software used. If selected, the LA100 sends a
break signal when a paper fault occurs.</P>
<H2 ID="S1.4">EIA Interface Information</H2>
<P>The terminal operates on full-duplex, asynchronous communication
lines. The EIA interface connector is a DB-25 male 25 pin
connector mounted on the back of the terminal (<A HREF="#F1-2">Figure 1-2</A>). The
LA100 EIA interface signals meet the EIA specification
requirements RS-232-C and the International Telephone and
Telegraph Consulting Committee (CCITT) recommendation V.24.</P>
<P CLASS="note">NOTE: The 20 mA current loop interface option allows the
terminal to be connected directly to a computer up to 305 m (1000
ft) away without the use of a modem.</P>
<TABLE ID="F1-2">
<CAPTION>Figure 1-2 EIA Connector</CAPTION>
<TBODY>
<TR>
<TD><IMG SRC="ma-7255.png" ALT=""></TD>
</TR>
</TBODY>
</TABLE>
<P><A HREF="#T1-1">Table 1-1</A> summarizes the EIA connector signals and the following
paragraphs explain each signal as used in the LA100. The
Communication Feature section explains the effect that the
communication features have on the EIA control signals.</P>
<DL>
<DT>Protective Ground -- Pin 1</DT>
<DD><P>This circuit is connected to the chassis of the terminal. It is
also connected to external grounds through the third wire of the
power cord.</P></DD>
<DT>Transmitted Data (TXD) -- Pin 2<BR>
Direction: From terminal</DT>
<DD><P>Signals on this circuit represent serially encoded characters that
are generated by the terminal.</P></DD>
<DT>Received Data (RXD) -- Pin 3<BR>
Direction: From terminal</DT>
<DD><P>Signals on this circuit represent serially encoded characters that
are generated by the user's equipment.</P></DD>
<DT>Request to Send (RTS) -- Pin 4<BR>
Direction: From terminal</DT>
<DD><P>When the RTS signal is on, the terminal intends to receive data.</P></DD>
<DT>Clear to Send (CTS) -- Pin 5<BR>
Direction: To terminal</DT>
<DD><P>This circuit monitors the CTS signal generated by the modem in
response to RTS. With modem control selected, the LA100 will not
transmit any codes if CTS is not on. With no modem control
selected, CTS is always assumed to be on.</P></DD>
<DT>Data Set Ready (DSR) -- Pin 6<BR>
Direction: To terminal</DT>
<DD><P>The DSR signal is on when the data set is ready. The terminal will
not transmit or receive data until this signal is on. With no
modem control selected, DSR is always assumed to be on. The DSR
indicator lights when the DSR signal is received.</P></DD>
<DT>Signal Ground -- Pin 7</DT>
<DD><P>This circuit establishes a common ground reference potential for
all interface circuits. This circuit is permanently connected to
the protective ground circuit.</P></DD>
<DT>Receive Line Signal Detect (RLSD) -- Pin 8<BR>
Direction: To terminal</DT>
<DD><P>When the RLSD signal is on, it indicates that the modem has
received the data carrier signal. The terminal will not receive
data until this signal is on. With no modem control selected, RLSD
is always assumed to be on.</P></DD>
<DT>Restraint (BUSY) -- Pin 11<BR>
Direction: From terminal</DT>
<DD><P>With restraint selected, the on condition of BUSY indicates that
the computer should temporarily stop sending data. When BUSY goes off,
the computer can resume sending data.</P></DD>
<DT>Speed Indicator (SPDI) -- Pin 12<BR>
Direction: To terminal</DT>
<DD><P>With speed mode selected, the terminal operates at the operator
selected baud rate when SPDI is off. The terminal operates at 1200
baud regardless of the operator selected rate when SPDI is on.</P></DD>
<DT>Secondary Request to Send (SRTS) -- Pin 19<BR>
Direction: From terminal</DT>
<DD><P>Same as restraint (pin 11)</P></DD>
<DT>Data Terminal Ready (DTR) -- Pin 20<BR>
Direction: From terminal</DT>
<DD><P>When the DTR signal is on, the terminal is capable of receiving
data. When DTR is off, the terminal is processing a disconnect or
the terminal is local.</P></DD>
<DT>Speed Indicator (SPDS) -- Pin 23<BR>
Direction: From terminal</DT>
<DD><P>With speed mode selected, and the receive baud rate of the
terminal is 1200 baud or higher, the terminal turns SPDS on.
Otherwise SPDS is kept off.</P></DD>
</DL>
<TABLE ID="T1-1">
<CAPTION>Table 1-1 EIA Interface Signals</CAPTION>
<THEAD>
<TR VALIGN="BOTTOM">
<TH>Pin</TH>
<TH>Name</TH>
<TH>Mnemonic</TH>
<TH>CCITT/EIA
Designation</TH>
<TH>Source</TH>
</TR>
</THEAD>
<TBODY>
<TR VALIGN="TOP">
<TD>1</TD>
<TD>Protective Ground</TD>
<TD>PGND</TD>
<TD>101/AA</TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>2</TD>
<TD>Transmitted Data</TD>
<TD>TXD</TD>
<TD>103/BA</TD>
<TD>LA100</TD>
</TR>
<TR VALIGN="TOP">
<TD>3</TD>
<TD>Received Data</TD>
<TD>RXD</TD>
<TD>104/BB</TD>
<TD>User</TD>
</TR>
<TR VALIGN="TOP">
<TD>4</TD>
<TD>Request to Send</TD>
<TD>RTS</TD>
<TD>105/CA</TD>
<TD>LA100</TD>
</TR>
<TR VALIGN="TOP">
<TD>5</TD>
<TD>Clear to Send</TD>
<TD>CTS</TD>
<TD>106/CB</TD>
<TD>User</TD>
</TR>
<TR VALIGN="TOP">
<TD>6</TD>
<TD>Data Set Ready</TD>
<TD>DSR</TD>
<TD>107/CC</TD>
<TD>User</TD>
</TR>
<TR VALIGN="TOP">
<TD>7</TD>
<TD>Signal Ground</TD>
<TD>SGND</TD>
<TD>102/AB</TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>8</TD>
<TD>Receive Line Signal Detect</TD>
<TD>RLSD</TD>
<TD>109/CF</TD>
<TD>User</TD>
</TR>
<TR VALIGN="TOP">
<TD>9</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>10</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>11</TD>
<TD>Restraint</TD>
<TD>BUSY</TD>
<TD></TD>
<TD>LA100</TD>
</TR>
<TR VALIGN="TOP">
<TD>12</TD>
<TD>Speed Indicator</TD>
<TD>SPDI</TD>
<TD>CI</TD>
<TD>User</TD>
</TR>
<TR VALIGN="TOP">
<TD>13</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>14</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>15</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>16</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>17</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>18</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>19</TD>
<TD>Secondary Request to Send</TD>
<TD>SRTS</TD>
<TD>120/SCA</TD>
<TD>LA100</TD>
</TR>
<TR VALIGN="TOP">
<TD>20</TD>
<TD>Data Terminal Ready</TD>
<TD>DTR</TD>
<TD>108.2/CD</TD>
<TD>LA100</TD>
</TR>
<TR VALIGN="TOP">
<TD>21</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>22</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>23</TD>
<TD>Speed Select</TD>
<TD>SPDS</TD>
<TD>111/CH</TD>
<TD>LA100</TD>
</TR>
<TR VALIGN="TOP">
<TD>24</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
<TR VALIGN="TOP">
<TD>25</TD>
<TD>No Connection</TD>
<TD></TD>
<TD></TD>
<TD></TD>
</TR>
</TBODY>
</TABLE>
<H2 ID="S1.5">EIA Circuit Jumpers</H2>
<P>The following EIA circuits can be physically disconnected by
removing a jumper:</P>
<UL>
<LI>Protective Ground - EIA connector Pin 1</LI>
<LI>Busy - EIA connector Pin 11</LI>
<LI>Speed Indicator - EIA connector Pin 12</LI>
<LI>Secondary Request to Send - EIA connector Pin 19</LI>
<LI>Speed Select - EIA connector Pin 23</LI>
</UL>
<P>When any of the EIA circuit jumpers are removed, the loopback
control line test fails. Refer to the jumper removal procedure in
the Installation guide to remove any of the EIA circuit jumpers.</P>
<H2 ID="S1.6">Connecting to the Computer</H2>
<P>The LA100 can be connected to a computer directly or through a
common carrier facility (telephone line) as shown in <A HREF="#F1-3">Figure 1-3</A>.
The EIA interface or optional 20mA current loop interface can be
used in both applications.</P>
<P>When connecting the terminal to the computer through the telephone
line, a modem (data set) is needed. The modem changes the serial
characters transmitted between the terminal and the computer into
signals that can be transmitted over the telephone lines. Several
types of modems can be used with the LA100. However, the modem
used by the terminal must be compatible with the modem used by the
computer.</P>
<P>The type of communication used by the terminal must also be
compatible with the computer and the communication system. The
type of communication used by the LA100 is operator selectable
(SET-UP is used for the Letterwriter 100, communication switches
are used for the Letterprinter 100).</P>
<TABLE ID="F1-3">
<CAPTION>Figure 1-3 Connecting to the Computer</CAPTION>
<TBODY>
<TR>
<TD><IMG SRC="ma-7776c.png" ALT=""></TD>
</TR>
</TBODY>
</TABLE>
<H2 ID="S1.7">Modem Control</H2>
<P>When on-line, the LA100 is connected to the communication line and
is capable of receiving and sending data. The terminal
communicates with EIA compatible devices on full duplex
asynchronous communication lines.</P>
<P>The terminal supports two basic types of full-duplex
communication; with or without modem control. Both methods allow
data to be transmitted and received at the same time. When
full-duplex with no modem control is selected, the data
transmission and reception is always enabled when not in local.
Full-duplex with modem control requires that both the terminal and
the modem recognize the proper EIA signals before transmitting
data. <A HREF="#T1-2">Table 1-2</A> shows the effect of the modem/no modem feature on
the EIA control signals.</P>
<P>No modem control allows the terminal to communicate directly with
a computer (null modem configurations) or with full-duplex modems
that do not support DSR (data set ready) or RLSD (receive line
signal indicator).</P>
<P>Modem control allows the terminal to communicate through modems
such as Bell 103, 212, Vadic 3400, or equivalent.</P>
<TABLE ID="T1-2">
<CAPTION>Table 1-2 Modem Control Effect on EIA Signals</CAPTION>
<THEAD>
<TR VALIGN="BOTTOM">
<TH>EIA Signal</TH>
<TH>No Modem</TH>
<TH>Modem Control</TH>
</TR>
</THEAD>
<TFOOT>
<TR VALIGN="TOP">
<TH>Key</TH>
<TD COLSPAN="2"></TD>
</TR>
<TR VALIGN="TOP">
<TD>Off</TD>
<TD COLSPAN="2">Signal off at EIA connector</TD>
</TR>
<TR VALIGN="TOP">
<TD>Active</TD>
<TD COLSPAN="2">Signal turns on or off depending on terminal state.</TD>
</TR>
<TR VALIGN="TOP">
<TD>On</TD>
<TD COLSPAN="2">Signal on at EIA connector</TD>
</TR>
<TR VALIGN="TOP">
<TD>Inactive</TD>
<TD COLSPAN="2">Signal ignored at EIA connector but terminal internally forces signal on.</TD>
</TR>
</TFOOT>
<TBODY>
<TR>
<TD>DTR</TD>
<TD>active</TD>
<TD>active</TD>
</TR>
<TR>
<TD>RTS</TD>
<TD>active</TD>
<TD>active</TD>
</TR>
<TR>
<TD>TXD</TD>
<TD>active</TD>
<TD>active</TD>
</TR>
<TR>
<TD>RXD</TD>
<TD>active</TD>
<TD>active</TD>
</TR>
<TR>
<TD>DSR</TD>
<TD>inactive</TD>
<TD>active</TD>
</TR>
<TR>
<TD>CTS</TD>
<TD>inactive</TD>
<TD>active</TD>
</TR>
<TR>
<TD>RLSD</TD>
<TD>inactive</TD>
<TD>active</TD>
</TR>
</TBODY>
</TABLE>
<H2 ID="S1.8">Full-Duplex Disconnect</H2>
<P>A full-duplex disconnect is accomplished by turning DTR (data
terminal ready) off for at least two seconds plus the DSR (data
set ready) delay time, but no greater than 3.8 seconds. The
following conditions cause a full-duplex disconnect.</P>
<UL>
<LI>DSR turns off after DTR is on</LI>
<LI>RLSD turns off for more than two seconds</LI>
<LI>Wrong number time out (DSR is on, then RLSD does not turn
on within 20 seconds)</LI>
<LI>If the paper fault switch is set to disconnect and a
paper out condition occurs</LI>
<LI>If the terminal is switched to local (for Letterprinter
100, press SELF TEST key; for Letterwriter 100, press
LINE/LOC key until LINE indicator goes off)</LI>
<LI>EOT control character received while coded disconnect is
enabled</LI>
</UL>
<H2 ID="S1.9">Input Buffer Overflow Prevention</H2>
<P>When the LA100 receives a character (other than the NUL and DEL
characters), the terminal stores the character in its 400
character input buffer. When the terminal is ready, characters
are removed from the input buffer and printed. If the terminal
falls behind by more than 400 characters, the input buffer
overflows. If an overflow occurs, the character is lost, a single
SUB control character is placed in the input buffer and the bell
tone sounds. There are three ways to avoid input buffer overflows.</P>
<OL>
<LI>Use the XON/XOFF or restraint feature to signal the data
source when to temporarily stop or resume sending data.
Using the XON/XOFF or restraint feature allows maximum
throughput and eliminates the need for fill character
calculations and message size limits. These features are
explained in detail later in this chapter.</LI>
<LI>Send data only as fast as it can be printed. When
receiving data at 1200 baud or less the terminal can keep
up with character reception. However, very short lines
and multiple form feeds are not processed this fast.
Also, characters received faster than 1200 baud cannot be
processed that quickly. In these cases, fill characters
are used to slow down the effective data transmission
speed. Fill time formulas are given in the following <A HREF="#S1.9.2">Fill
Time Formulas</A> section.</LI>
<LI>Limit the number of characters in the message to the
terminal's input buffer size. If the buffer is empty at
the beginning of the transmission, the terminal can
receive a message of 400 characters without a buffer
overflow.</LI>
</OL>
<H3 ID="S1.9.1">XON/XOFF and Restraint</H3>
<P>The XON/XOFF and restraint features are used to prevent input
buffer overflows. When XON/XOFF and/or restraint is selected, the
terminal constantly monitors the number of characters stored in
the input buffer. The terminal signals the computer to stop
sending data (sends XOFF control character or sets the restraint
signal off) when any of the following conditions occur:</P>
<UL>
<LI>Number of characters in the input buffer exceeds 200
characters</LI>
<LI>Terminal transmits XOFF and then receives 60 characters</LI>
</UL>
<P>The terminal signals the computer to resume data transmission
(sends XON control character or sets the restraint signal on)
when any of the following conditions occur:</P>
<UL>
<LI>When the number of characters in the input buffer is less
than 60 characters</LI>
<LI>Terminal is switched on-line (or powered up on-line)</LI>
</UL>
<P>XON/XOFF and restraint are operator selectable features.</P>
<H3 ID="S1.9.2">Fill Time Formulas</H3>
<P>When receiving data at 1200 baud or less, the terminal can keep up
with normal character reception. Very short lines and multiple
form feeds cannot be printed this fast. Fill characters may be
used to slow down the effective data transmission speed in these
cases. Fill characters do not enter the input buffer they are
stripped out of the data stream upon reception.</P>
<P>The terminal's printhead and form movements (horizontal and
vertical) terminal are directly related to the fill time required
to slow down the effective data transmission speed. The fill time
required to compensate for these movements can be converted to the
number of fill characters needed using the following formula.</P>
<PRE>                                Fill Time Required
Number of Fill Characters = --------------------------
                             Character Execution Time</PRE>
<P CLASS="note">NOTE: NUL is the only recommended fill character even though
some other characters may seem to achieve the same result in
special cases.</P>
<H3 ID="S1.9.3">Determining Fill Time Required</H3>
<P>Required fill time for horizontal movement (including tabs and
positioning sequences) is determined in the following way.</P>
<P>First figure the actual number of columns moved. Then, allow 15 ms
for each of the first 10 columns (30 ms in double-width pitches:
5, 6, 6.6, 8.25) and 5.5 ms for each additional column (11 ms in
double-width pitches).</P>
<P>Required fill time for vertical movement (includes linefeeds,
vertical tabs, form feeds, and vertical positioning sequences) is
determined in the following way.</P>
<P>First convert the number of lines moved to actual distance moved
using the following formula.</P>
<PRE>                  Number of Lines Moved
Inches Moved  =  -----------------------
                     Vertical Pitch</PRE>
<P>Then allow 38 ms for the first line moved up to 1/6 inch, and 200
ms for each additional inch.</P>
<H3 ID="S1.9.4">Character Execution Time</H3>
<P>The character execution time is given in milliseconds and is based
on a given baud rate. It is the time the computer takes to slow
down the effective data transmission speed to the terminal.
Character execution times at the applicable baud rates are shown
in <A HREF="#T1-3">Table 1-3</A>.</P>
<TABLE ID="T1-3">
<CAPTION>Table 1-3 Character Execution Times</CAPTION>
<COL WIDTH="5em" ALIGN="RIGHT">
<COL WIDTH="100%" ALIGN="LEFT">
<THEAD>
<TR>
<TH>Baud Rate</TH>
<TH>Execution Times (msec)</TH>
</TR>
</THEAD>
<TFOOT>
<TR>
<TD COLSPAN="2" ALIGN="LEFT"><P CLASS="note">NOTE: Character execution times are provided for calculation of
fill times only.</P></TD>
</TR>
</TFOOT>
<TBODY>
<TR>
<TD>110</TD>
<TD>90.0</TD>
</TR>
<TR>
<TD>300</TD>
<TD>33.3</TD>
</TR>
<TR>
<TD>600</TD>
<TD>16.6</TD>
</TR>
<TR>
<TD>1200</TD>
<TD>8.3</TD>
</TR>
<TR>
<TD>1800</TD>
<TD>5.5</TD>
</TR>
<TR>
<TD>2400</TD>
<TD>4.1</TD>
</TR>
<TR>
<TD>4800</TD>
<TD>2.0</TD>
</TR>
<TR>
<TD>9600</TD>
<TD>1.0</TD>
</TR>
</TBODY>
</TABLE>
<H3 ID="S1.9.5">Fill Time Formula Examples</H3>
<OL>
<LI>Horizontal Movement
<P>Assumed values: Baud Rate = 1200, Horizontal Pitch = any
single width pitch (10, 12, 13.2, 16.5). Also assume that
horizontal tab stops are set at columns 9, 17, and 25 and
printing begins at column 9. If the next two characters
received are TAB TAB, calculate the number of fill
characters required in the following way.</P>
<P>First, calculate the number of columns moves using the
following formula.</P>
<PRE>Final Column - Current Column = Number Columns Moved

                       25 - 9 = 16</PRE>
<P>Then allow 15 ms per column for the first 10 columns and
5.5 ms per column for the remaining columns.</P>
<P>15 ms &times; 10 = 150 ms</P>
<P>5.5 ms &times; 6 = 33 ms</P>
<P>150 + 33 ms = 183 ms</P>
<P>The fill time required is 183 ms.</P>
<P>Next, divide the fill time required by the character
execution time found in <A HREF="#T1-3">Table 1-3</A>.</P>
<PRE>                                     183 ms
Number Fill Characters Required  =  --------
                                     8.3 ms</PRE>
<P>The number of fill characters required is 22.04. Round
this number off to the next whole number, which is 23.
Twenty three (23) fill characters (NUL) should follow the
two tabs.</P></LI>
<LI>Vertical Movement
<P>Assumed values: Baud Rate = 1200 baud, Vertical Pitch = 6
lines per inch and paper is set to line 10. Also assume
the next characters received are nine line feeds.</P>
<P>First, calculate the actual distance moved using the
following formula.</P>
<PRE>                          Lines Moved
Number Inches Moved  =  ----------------
                         Vertical Pitch

                         9
          1&frac12; inches  =  ---
                         6</PRE>
<P>Then allow 38 ms for the first 1/6 inch moved and 200 ms
for the remaining number of inches moved.</P>
<P>200 ms &times; 1 2/6 inches = 266 ms</P>
<P>266 ms + 38 ms = 304 ms.</P>
<P>The fill time required is 304 ms.</P>
<P>Next, divide the fill time required by the character
execution time found in <A HREF="#T1-3">Table 1-3</A>.</P>
<PRE>                                     304 ms
Number fill characters required  =  --------
                                     8.3 ms</PRE>
<P>The number of fill characters required is 36.62. Round
this number off to the next whole number, which is 37.
Thirty seven (37) fill characters (NUL) should follow the
nine line feeds.</P></LI>
</OL>
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